The present application claims priority to Japanese Applications No. P11-297297 filed Oct. 19, 1999, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a micro mirror apparatus which is a sub-component consisting of a small mirror and an optical disk apparatus used as a jogging actuator to serve as a tracking servo mechanism for this micro mirror.
2. Description of Related Art
In recent years in the field of electric machinery, technologies related to the semi-conductor manufacturing process are frequently applied to develop a technology called MEMS (Micro Electro Mechanical System) designed to miniaturize various mechanical elements.
Mechanical elements miniaturized by such MEMS technology are called micro-mechanical devices. Among them a device in which a mirror as a mechanical element designed to reflect light is miniaturized is a micro mirror apparatus.
As a micro mirror apparatus, one comprising a stationary part and a movable part having a reflecting surface all of which are joined together by at least a hinge part has already been developed. On the movable part on the opposite side of the reflecting surface, a part that functions for example as an electrode for an Al film is provided. And on the stationary part, at a position opposite through an air gap to a part that functions as an electrode for the movable part a pair of electrodes for Al films are provided.
This micro mirror apparatus alternatively applies different signal voltages to a pair of electrodes on Al films provided on the stationary part and creates alternatively opposite electrostatic force between this pair of electrodes and the part that functions as an electrode provided on the movable part to deform by torsion a hinge part and pivot the movable part on this hinge part as its axis, so that the reflecting surface formed on the movable part may incline in optional directions.
Incidentally, in recent years a technology has been proposed for using a micro mirror apparatus of the above-mentioned construction as a jogging actuator to serve as a tracking servo mechanism of the optical disk apparatus. In order to enable this micro mirror apparatus to demonstrate an outstanding performance as a jogging actuator of optical disks, it is desirable that the micro mirror has a vibration characteristic in that the primary natural frequency and the secondary natural frequency are far apart, in other word the servo band is wide.
In the micro mirror apparatus of the above-mentioned construction, the vibration mode shape and natural frequency result from the construction of the hinge part. To be more specific, the primary natural frequency that causes the movable part to pivot in the primary vibration mode results from the torsional rigidity of the hinge part, and the secondary natural frequency that causes the out-of-plane vibrations of the movable part in the secondary vibration mode results from the flexural rigidity of the hinge part.
Therefore, in the micro mirror apparatus of the above-mentioned construction, in order to separate the primary natural frequency and the secondary natural frequency and to widen the servo band, it is effective to enhance only the flexural rigidity of the hinge part without causing any change in the torsional rigidity of the hinge part.
However, the torsional rigidity and flexural rigidity of the hinge part are dependent each other, and particularly when the hinge part has a rectangular or square cross section, the degree of such dependency is high. Therefore, when the hinge part has a rectangular or square cross section, any attempt to enhance the flexural rigidity of the hinge part automatically results in a higher torsional rigidity of the hinge part, and it is difficult to widen the servo band of the micro mirror apparatus.
It is therefore an object of the present invention to provide a micro mirror apparatus having a widened servo band.
It is another object of the present invention to provide an optical disk apparatus in which this micro mirror apparatus is used as a jogging actuator.
The micro mirror apparatus according to the present invention is a micro mirror apparatus including a stationary part, a movable part connected to the stationary part through a hinge part, and a reflecting surface formed on the movable part, the movable part pivoting on the hinge part as its axis by torsional deformation of the hinge part, wherein on at least a part of the hinge part a protrusion protruding in the direction of its thickness is formed.
In this micro mirror apparatus, the formation of a protrusion protruding in the thickness direction on the hinge part greatly increases the flexural rigidity of the hinge part in comparison with any increase in the torsional rigidity of the hinge part. Therefore, in this micro mirror apparatus, the separation of the primary natural frequency and the secondary natural frequency widens the servo band.
And another micro mirror apparatus according to the present invention is a micro mirror apparatus including a stationary part, a movable part connected to the stationary part through a hinge part, and a reflecting surface formed on the movable part, the movable part pivoting on the hinge part as its axis by torsional deformation of the hinge part.
And in this micro mirror apparatus, at least one of the edge connected to the stationary part of the hinge part or the edge connected to the movable part is made line symmetrically polygonal or curved surface shaped along the central axis of torsional deformation of the hinge part as its axis of symmetry.
In this micro mirror apparatus, at least one of the edge connected to the stationary part of the hinge part or the edge connected to the movable part is made line symmetrically polygonal or curved surface along the central axis of torsional deformation of the hinge part as its axis of symmetry, and this fact greatly enhances the flexural rigidity of the hinge part in comparison with any increase in the torsional rigidity of the hinge part. Therefore, the separation of the primary natural frequency and the secondary natural frequency widens the servo band.
And the optical disk apparatus according to the present invention is an optical disk apparatus for recording and/or reproducing information on an optical disk by irradiating light emitted from the light source onto the optical disk and includes a micro mirror apparatus that reflects the light emitted from the light source and irradiate the same onto the optical disk.
In this optical disk apparatus, the micro mirror apparatus includes a stationary part, a movable part connected to the stationary part through a hinge part, and a reflecting surface formed on this movable part, and the movable part pivoting on the hinge part as its axis by torsional deformation of the hinge part shifts the position of the light spot reflected by the reflecting surface and irradiated on the optical disk.
And in this micro mirror apparatus, on at least a part of the hinge part a protrusion protruding in the direction of its thickness is formed.
The formation of a protrusion protruding in the direction of thickness on the hinge part of the micro mirror apparatus in this optical disk apparatus greatly enhances the flexural rigidity of the hinge part in comparison with any increase in the torsional rigidity of the hinge part and widens the servo band. And this feature enables this micro mirror apparatus to demonstrate its outstanding performance as a jogging actuator and to serve as a precise tracking servo mechanism.
And another optical disk apparatus according to the present invention is an optical disk apparatus for recording and/or reproducing information on an optical disk by irradiating light emitted from the light source onto the optical disk including a micro mirror apparatus that reflects the light emitted from the light source and irradiate the same onto the optical disk.
In this optical disk apparatus, the micro mirror apparatus includes a stationary part, a movable part connected to the stationary part through a hinge part, and a reflecting surface formed on this movable part, and the movable part pivoting on the hinge part as its axis by torsional deformation of the hinge part shifts the position of the light spot reflected by the reflecting surface and irradiated on the optical disk.
And in this micro mirror apparatus, at least one of the edge connected to the stationary part of the hinge part or the edge connected to the movable part is made line symmetrically polygonal or curved surface shaped along the central axis of torsional deformation as its axis of symmetry.
In this optical disk apparatus, at least one of the edge part connected to the stationary part or the edge part connected to the movable part of the hinge part of the micro mirror apparatus is made line symmetrically polygonal or curved surface shaped along the central axis of torsional deformation of the hinge part as the axis of symmetry, and this fact considerably enhances the flexural rigidity of the hinge part in comparison with an increased torsional rigidity of the hinge part and therefore enables this micro mirror apparatus to demonstrate its outstanding performance as a jogging actuator and to serve as a precise tracking servo mechanism.
The micro mirror apparatus of the present invention enhances greatly only the flexural rigidity of the hinge part without causing any significant change in its torsional rigidity thus leading to a wider servo band.
And the optical disk apparatus of the present invention which uses a micro mirror apparatus having a wider servo band as a jogging actuator improves its track following performance and enables to realize high-speed accesses. And this optical disk apparatus can narrow recording tracks and therefore can realize a high-density record reproduction.